1. Field of the Invention
The present invention relates generally to a control system for an automatic transmission for automotive vehicles. Specially, the invention relates to a system which, in an emergency, is capable of locking the gear train of the vehicles having an automatic transmissions, which system so as to prevent unintended sudden acceleration of the vehicle from occurring by erroneous operation at a relatively low vehicle speed of less than 10 km/hr., for example.
2. Description of the Prior Art
Conventionally, an automatic transmission includes a torque converter, an oil pump, a power train or a gear train, a hydraulic control system having a control valve, and an electronic control system.
The gear train of automatic transmission includes a plurality of frictional elements for operating so as to establish or release engagement between a set of planetary gears or between individual elements of the planetary gears. The engagement between frictional elements is established or released by hydraulic pressure provided from the control valve.
The respective range modes of the automatic transmission can be selected by manually operating a select lever adjacent to a driver seat. The setting of the select lever is transmitted through transmitting members, such as a wire cable, a rod, or a lever to the control valve with the result that the control valve is operated and outputs a line pressure.
Generally, a vehicle having such automatic transmissions will move immediately, when the select lever is changed from a non-driving position, such as neutral position (N) or parking position (P) to driving position, such as drive position (D) or reverse position (R). Therefore, switching the lever from non-driving position to driving position is preferably performed with the brake ON, and thereafter the brakes are released to allow the vehicle to accelerate gradually.
Conversely, if the control lever is operated to a drive position while the engine is under full throttle the vehicle will accelerate suddenly and violently. As a result, passengers may not only be surprised but also may be exposed to great danger.
Therefore, there have been proposed transmission control systems wherein the transmission will not go into gear if the brakes are not applied and the engine is rotating quickly.
One such transmission control system has been disclosed in the Japanese Utility Model Publication (Jikkou Showa) 62-20343. In this and other conventional transmission control systems, the shift preventing means comprises a solenoid coil and a solenoid shaft. The shift preventing means is attached on an outer member outside of the transmission assembly, such as a select lever bracket.
As set forth above, the movement of the select lever is transmitted through the transmitting members to the control valve. The transmitting members are designed to have a suitable degree of play such that the linkages can move smoothly. Therefore, even if the select lever is locked by the preventing means, the select lever move slightly from the predetermined position. Therefore, with this construction, the select lever is not perfectly locked.
In order to overcome the problems in the prior art and increase the performance of the running control systems, there has been proposed an improved running system which reliably prevents such erroneous operation of the select lever by the driver.